1. Field of the Invention
The present invention relates to a low-voltage current reference, and more particularly, a low-voltage current reference providing a current being substantially constant with temperature.
2. Description of the Prior Art
Prior power references—current references and voltage references, for example—are subject to variances with temperature, affecting the performance of the circuits being powered by them. Many timers and other high-accuracy circuits and chips, however, require current references that are insensitive to fluctuations in temperature.
A bandgap reference is a common analog circuit used as a stable voltage reference for low-voltage circuits. In normal practice, as shown in FIG. 1 according to related art, a standard bandgap 140 can be used to produce a current that is proportional to absolute temperature (PTAT) Iptat. Another a low voltage bandgap 120 is used to produce a constant voltage that yields a complementary to absolute temperature (CTAT) current Icmnres when applied over a resistor in the current summer. When the ratio between the PTAT and CTAT currents (Iptat and Icmnres) are chosen properly and combined, the significant effects of the temperature dependency cancel out, resulting in a current Iconst that is effectively temperature insensitive. The current from the PTAT current bandgap is combined with the Icmnres current (in the current summer 130), to create a resultant current that is constant with temperature (CWT) Iconst.
There are, however, a number of problems and inconveniences from the above. The bandgaps 120 and 140 take up significant real estate on a circuit, and consume considerable power themselves. Additionally, each of the above bandgaps 120 and 140 requires a start circuit (115 and 110, respectively) to ensure they operate properly and in a timely fashion. These start circuits 115 and 110 occupy circuitry real estate and also consume power. From these issues, then, it becomes clear there remains room for improvement in the arena of temperature-insensitive current sources.